23G 
ON THE NITROGEN OF PLANTS. 
numerous transformations. We have now only to consider 
whether it really is taken up in the form of ammonia by the 
roots of plants, and in that form applied to their organs to 
the production of the azotized matters contained in them. 
This question is susceptible of easy solution, by well-known 
facts. 
In the year 1834, I was engaged with Dr. Wilbrand, Pro- 
fessor of Botany in the University of Giessen, in an investiga- 
tion respecting the quantity of sugar contained in different 
varieties of maple-trees, which grew upon soils which were 
not manured. We obtained crystallized sugars from all, by 
simply evaporating their juices, without the addition of any 
foreign substances ; and we unexpectedly made the observa- 
tion, that a great quantity of ammonia was emitted from this 
juice, when mixed with lime, and also from the sugar itself 
during its refinement. The vessels, which hung upon the 
trees in order to collect the juice, were watched with great 
attention, on account of the suspicion that some evil-disposed 
persons had introduced urine into them, but still a large 
quantity of ammonia was again found in the form of neutral 
salts. The juice had no color, and had no reaction on that 
of vegetables. Similar observations were made upon the 
juice of the birch-tree; the specimens subjected to experiment 
were taken from a wood, several miles, distant from any house, 
and yet the clarified juice, evaporated with lime, emitted a 
strong odor of ammonia. 
In the manufactories of beet-root sugar, many thousand 
cubic feet of juice are daily purified with lime, in order to 
free it from vegetable albumen and gluten, and it is after- 
wards evaporated for crystallization. Every person, who 
has entered such a manufactory, must have been astonished 
at the great quantity of ammonia which is volatilized along 
with the steam. This ammonia must be contained in the 
form of an ammoniacal salt, because the neutral juice possesses 
the same characters as the solution of such a salt in water ; 
it acquires, namely, an acid reaction during evaporation, in 
